feat: cross-platform date handling with GNU/BSD/python3 support

Create scripts/lib/date-compat.sh with date_today, date_yesterday,
date_to_epoch, date_days_ago, and date_now_iso helpers.
All dates use UTC consistently.

Closes DOJ-2430

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: dbejarano820

scripts/lib/date-compat.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+# Cross-platform date utilities for CodeSensei
+# Supports: GNU date (Linux), BSD date (macOS), python3 fallback
+
+# Get today's date in YYYY-MM-DD format (UTC)
+date_today() {
+  date -u '+%Y-%m-%d' 2>/dev/null || python3 -c "from datetime import datetime; print(datetime.utcnow().strftime('%Y-%m-%d'))"
+}
+
+# Get yesterday's date in YYYY-MM-DD format (UTC)
+date_yesterday() {
+  # Try GNU date first
+  date -u -d 'yesterday' '+%Y-%m-%d' 2>/dev/null && return
+  # Try BSD date (macOS)
+  date -u -v-1d '+%Y-%m-%d' 2>/dev/null && return
+  # Python fallback
+  python3 -c "from datetime import datetime, timedelta; print((datetime.utcnow() - timedelta(days=1)).strftime('%Y-%m-%d'))" 2>/dev/null && return
+  # Last resort: empty string
+  echo ""
+}
+
+# Convert date string (YYYY-MM-DD) to epoch seconds
+date_to_epoch() {
+  local date_str="$1"
+  # Try GNU date
+  date -u -d "$date_str" '+%s' 2>/dev/null && return
+  # Try BSD date (macOS)
+  date -u -j -f '%Y-%m-%d' "$date_str" '+%s' 2>/dev/null && return
+  # Python fallback
+  python3 -c "from datetime import datetime; print(int(datetime.strptime('$date_str', '%Y-%m-%d').timestamp()))" 2>/dev/null && return
+  echo "0"
+}
+
+# Get date N days ago in YYYY-MM-DD format (UTC)
+date_days_ago() {
+  local days="$1"
+  # Try GNU date
+  date -u -d "${days} days ago" '+%Y-%m-%d' 2>/dev/null && return
+  # Try BSD date (macOS)
+  date -u -v-${days}d '+%Y-%m-%d' 2>/dev/null && return
+  # Python fallback
+  python3 -c "from datetime import datetime, timedelta; print((datetime.utcnow() - timedelta(days=${days})).strftime('%Y-%m-%d'))" 2>/dev/null && return
+  echo ""
+}
+
+# Get current UTC timestamp in ISO format
+date_now_iso() {
+  date -u '+%Y-%m-%dT%H:%M:%SZ' 2>/dev/null || python3 -c "from datetime import datetime; print(datetime.utcnow().strftime('%Y-%m-%dT%H:%M:%SZ'))"
+}

scripts/quiz-selector.sh

@@ -19,6 +19,10 @@ PROFILE_FILE="$PROFILE_DIR/profile.json"
 PLUGIN_ROOT="${CLAUDE_PLUGIN_ROOT:-$(dirname "$(dirname "$0")")}"
 QUIZ_BANK="$PLUGIN_ROOT/data/quiz-bank.json"
 
+# Source cross-platform date helpers
+# shellcheck source=scripts/lib/date-compat.sh
+source "$PLUGIN_ROOT/scripts/lib/date-compat.sh"
+
 # Default output if we can't determine anything
 DEFAULT_OUTPUT='{"mode":"dynamic","concept":null,"reason":"No profile data available","static_question":null,"belt":"white","quiz_format":"multiple_choice"}'
 
@@ -40,8 +44,8 @@ SESSION_CONCEPTS=$(jq -c '.session_concepts // []' "$PROFILE_FILE")
 TOTAL_QUIZZES=$(jq -r '.quizzes.total // 0' "$PROFILE_FILE")
 CORRECT_QUIZZES=$(jq -r '.quizzes.correct // 0' "$PROFILE_FILE")
 
-TODAY=$(date -u +%Y-%m-%d)
-NOW_EPOCH=$(date +%s)
+TODAY=$(date_today)
+NOW_EPOCH=$(date_to_epoch "$TODAY")
 
 # Determine quiz format based on belt level
 # Orange Belt+ gets a mix of formats; lower belts get multiple choice
@@ -84,8 +88,8 @@ if [ "$QUIZ_HISTORY" != "[]" ]; then
 
     # Calculate days since last wrong answer
     LAST_WRONG_DATE=$(echo "$LAST_WRONG" | cut -d'T' -f1)
-    LAST_EPOCH=$(date -j -f "%Y-%m-%d" "$LAST_WRONG_DATE" +%s 2>/dev/null || date -d "$LAST_WRONG_DATE" +%s 2>/dev/null)
-    if [ -n "$LAST_EPOCH" ]; then
+    LAST_EPOCH=$(date_to_epoch "$LAST_WRONG_DATE")
+    if [ -n "$LAST_EPOCH" ] && [ "$LAST_EPOCH" != "0" ]; then
       DAYS_SINCE=$(( (NOW_EPOCH - LAST_EPOCH) / 86400 ))
     else
       DAYS_SINCE=999

scripts/session-start.sh

@@ -5,7 +5,13 @@
 PROFILE_DIR="$HOME/.code-sensei"
 PROFILE_FILE="$PROFILE_DIR/profile.json"
 SESSION_LOG="$PROFILE_DIR/sessions.log"
-TODAY=$(date -u +%Y-%m-%d)
+PLUGIN_ROOT="${CLAUDE_PLUGIN_ROOT:-$(dirname "$(dirname "$0")")}"
+
+# Source cross-platform date helpers
+# shellcheck source=scripts/lib/date-compat.sh
+source "$PLUGIN_ROOT/scripts/lib/date-compat.sh"
+
+TODAY=$(date_today)
 
 # Create profile directory if it doesn't exist
 mkdir -p "$PROFILE_DIR"
@@ -17,7 +23,7 @@ if [ ! -f "$PROFILE_FILE" ]; then
   "version": "1.0.0",
   "plugin": "code-sensei",
   "brand": "Dojo Coding",
-  "created_at": "$(date -u +%Y-%m-%dT%H:%M:%SZ)",
+  "created_at": "$(date_now_iso)",
   "belt": "white",
   "xp": 0,
   "streak": {
@@ -45,7 +51,7 @@ if [ ! -f "$PROFILE_FILE" ]; then
       "id": "first-session",
       "name": "First Steps",
       "description": "Started your first CodeSensei session",
-      "earned_at": "$(date -u +%Y-%m-%dT%H:%M:%SZ)"
+      "earned_at": "$(date_now_iso)"
     }
   ],
   "preferences": {
@@ -73,7 +79,7 @@ if command -v jq &> /dev/null; then
     NEW_STREAK=$CURRENT_STREAK
   elif [ -n "$LAST_SESSION" ]; then
     # Check if last session was yesterday
-    YESTERDAY=$(date -u -d "yesterday" +%Y-%m-%d 2>/dev/null || date -u -v-1d +%Y-%m-%d 2>/dev/null)
+    YESTERDAY=$(date_yesterday)
     if [ "$LAST_SESSION" = "$YESTERDAY" ]; then
       NEW_STREAK=$((CURRENT_STREAK + 1))
     else
@@ -107,7 +113,7 @@ if command -v jq &> /dev/null; then
   echo "$UPDATED" > "$PROFILE_FILE"
 
   # Log session
-  echo "$TODAY $(date -u +%H:%M:%S) session_start" >> "$SESSION_LOG"
+  echo "$(date_now_iso) session_start" >> "$SESSION_LOG"
 
   # Show streak info if notable
   BELT=$(jq -r '.belt // "white"' "$PROFILE_FILE")